Baffles are provided in heat exchangers to increase the
(A) Fouling factor
(B) Heat transfer area
(C) Heat transfer co-efficient
(D) Heat transfer rate
Description : Pick out the wrong statement. (A) Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient (B) In a shell and tube heat exchanger ... surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube
Last Answer : (C) S.I. unit of fouling factor is Watt/m2 .°K
Description : Baffles provided on the shell side of a shell and tube heat exchanger are meant for (A) Providing support for the tubes (B) Improving heat transfer (C) Both 'a' & 'b' (D) Preventing the fouling of tubes & stagnation of shell side fluid
Last Answer : C) Both 'a' & 'b'
Description : The overall heat transfer co-efficient for a shell and tube heat exchangerfor clean surfaces is U0 = 400 W/m2 .K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m2 .K. The overall heat transfer coefficient ... 1200 W/m2 .K (B) 894 W/m2 .K (C) 333 W/m2 .K (D) 287 W/m2 .K
Last Answer : (C) 333 W/m2 .K
Description : Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface). (A) U1 - U2 (B) 1/U1 - 1/U2 (C) 1/U2 - 1/U1 (D) U2 - U1
Last Answer : (B) 1/U1 - 1/U2
Description : Baffles in the shell side of a shell and tube heat exchanger (A) Increase the cross-section of the shell side liquid (B) Force the liquid to flow parallel to the bank (C) Increase the shell side heat transfer co-efficient (D) Decrease the shell side heat transfer co-efficient
Last Answer : (C) Increase the shell side heat transfer co-efficient
Description : Double pipe heat exchangers are preferably useful, when (A) High viscosity liquid is to be cooled (B) Requirement of heat transfer area is low (C) Overall heat transfer co-efficient is very high (D) A corrosive liquid is to be heated
Last Answer : (B) Requirement of heat transfer area is low
Description : Heat exchangers operating, when the asymptotic range is reached, (A) Provide very large heat transfer co-efficient (B) Results in making part of the heating surface inactive (C) Results in abruptly increased velocity (D) None of these
Last Answer : (B) Results in making part of the heating surface inactive
Description : Indirect contact heat exchangers are preferred over direct contact heat exchangers, because (A) Heat transfer co-efficient are high (B) There is no risk of contamination (C) There is no mist formation (D) Cost of equipment is lower
Last Answer : (B) There is no risk of contamination
Description : Multipass heat exchangers are used (A) Because of simplicity of fabrication (B) For low heat load (C) To obtain higher heat transfer co-efficient and shorter tube (D) To reduce the pressure drop
Last Answer : (C) To obtain higher heat transfer co-efficient and shorter tube
Description : Use of transverse baffles in a shell and tube heat exchanger is done to increase the (A) Rate of heat transfer (B) Flow velocity (C) Turbulence of shell side fluid (D) All (A), (B) and (C)
Last Answer : (D) All (A), (B) and (C)
Description : For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of (A) 1 (B) 1.74 (C) 6.1 (D) 37
Last Answer : (C) 6.1
Description : The main purpose of providing fins on heat transfer surface is to increase the (A) Temperature gradient (B) Mechanical strength of the equipment (C) Heat transfer area (D) Heat transfer co-efficient
Last Answer : (C) Heat transfer area
Description : Pick out the wrong statement. (A) In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2 (B) Sherwood number in mass transfer corresponds to ... tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side
Last Answer : (C) Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger
Description : Heat transfer rate per unit area is called (A) Thermal conductivity (B) Heat flux (C) Heat transfer co-efficient (D) Thermal diffusivity
Last Answer : (B) Heat flux
Description : Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger? (A) Tube side pressure drop and the heat transfer rate (B) Convective heat transfer co-efficient (C) Effective tube surface area for convective heat transfer (D) All (A) (B) and (C)
Last Answer : (D) All (A) (B) and (C)
Description : Double pipe heat exchangers are used (A) When heat transfer area required is very high (B) When heat transfer area required is very low, i.e. (100-200 ft 2 ). (C) Because it occupies less floor area (D) Because it is less costly
Last Answer : (B) When heat transfer area required is very low, i.e. (100-200 ft 2 )
Description : Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both ... steam on shell side (D) Shell and tube heat exchanger with air on shell side and steam inside tubes
Last Answer : (B) Finned tube heat exchanger with air outside and steam inside
Description : The main function of baffles provided in a shell and tube heat exchanger is to (A) Facilitate the cleaning of outer tube surface (B) Enhance turbulence (C) Hold the tubes in position (D) All 'a', 'b' & 'c'
Last Answer : (B) Enhance turbulence
Description : Baffles in mixing tanks are provided to (A) Reduce swirling and vortex formation (B) Increase the structural strength of the tank (C) Aid in rotational flow (D) None of these
Last Answer : (A) Reduce swirling and vortex formation
Description : Overall heat transfer co-efficient of a particular tube is U1 . If the same tube with some dirt deposited on either side has coefficient U2 , then (A) U1 = U2 (B) U2 > U1 (C) U1 > U2 (D) U1 = dirt factor - U2
Last Answer : (A) U1 = U2
Description : In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in (A) Reducing the axial mixing (B) Increasing the rate of extraction (C) Maintaining the concentration difference between the two phases (D) All 'a', 'b' & 'c'
Last Answer : (D) All 'a', 'b' & 'c'
Description : Pick out the wrong statement. (A) Heat transfer by radiation cannot occur across an absolute volume (B) In case of a shell and tube heat exchanger, the pressure drop through the shell is ... The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is the same
Last Answer : (A) Heat transfer by radiation cannot occur across an absolute volume
Description : As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient (A) Continues to increase (B) Continues to decrease (C) Goes through a minimum (D) Goes through a maximum
Last Answer : (C) Goes through a minimum
Description : In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient (A) Increases (B) Decreases (C) Is not affected (D) May increase or decrease; depends on the feed
Last Answer : (B) Decreases
Description : A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0 ... that of the un-insulated steam pipe (D) Less than the steam pipe with 5 cms insulation
Last Answer : (B) Less than that of the un-insulated steam pipe
Description : . The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The ambient air is at 30°C ... from the outer surface in W.m-2 is (A) 165.4 (B) 167.5 (C) 172.5 (D) 175
Last Answer : (A) 165.4
Description : Out of the following four assumptions used in the derivation of theequation for LMTD [LMTD = (∆t1 - ∆t2 )/ln(∆t1 /∆t2 )], which one is subject to the largest deviation in practice ? (A) Constant ... (B) Constant rate of fluid flow (C) Constant specific heat (D) No partial phase change in the system
Last Answer : (B) Constant rate of fluid flow
Description : A thin, flat & square plate measuring 2 m 2 m is freely hanging in ambient air at 25°C. It is exposed to the solar radiation falling on one side of the plate at the rate of 500 W/m2. The plate temperature will ... heat transfer co-efficient is __________ W/m2 °C. (A) 50 (B) 100 (C) 150 (D) 200
Last Answer : (B) 100
Description : . A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because (A) Total heat transfer area of ... in a single effect is much lower than that in any effect in a multi-effect system
Last Answer : (B) Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
Description : 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the ... will be (A) 15 min (B) 22 min (C) 44 min (D) 51 min
Last Answer : (D) 51 min
Description : Pick out the wrong statement. (A) 'Solvates' are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a 'hydrate' (B) In heat exchanger ... vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area
Last Answer : (C) Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted
Description : Fouling factor' used in the design of a multipass shell and tube heat exchanger is a (A) Non-dimensional factor (B) Factor of safety
Last Answer : (B) Factor of safety
Description : Fouling factor (A) Is a dimensionless quantity (B) Does not provide a safety factor for design (C) Accounts for additional resistances to heat flow (D) None of these
Last Answer : (C) Accounts for additional resistances to heat flow
Description : _________ baffles are provided in ball mills. (A) Horizontal (B) No (C) Only two (D) None of these
Last Answer : (A) Horizontal
Description : In a heat exchanger, floating head is provided to (A) Facilitate cleaning of the exchanger (B) Increase the heat transfer area (C) Relieve stresses caused by thermal expansion (D) Increase log mean temperature gradient
Last Answer : (C) Relieve stresses caused by thermal expansion
Description : LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface ... Parallel (B) Mixed (C) Counter flow (D) Same in either 'a', b' or 'c'
Last Answer : (D) Same in either 'a', b' or 'c'
Description : Finned tube heat exchangers (A) Give larger area per tube (B) Use metal fins of low thermal conductivity (C) Facilitate very large temperature drop through tube wall (D) Are used for smaller heat load
Last Answer : (A) Give larger area per tube
Description : An ideal coolant for a nuclear reactor should (A) Be a good absorber of neutrons (B) Be capable of attaining high temperature, only when it is pressurised (C) Have high density, but low heat transfer co-efficient (D) Be free from radiation damage and non-corrosive
Last Answer : (D) Be free from radiation damage and non-corrosive
Description : Pick out the wrong statement. (A) The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation ( ... in a heat exchanger is controlled by the value of the film co-efficient, which is higher
Last Answer : (D) Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film co-efficient, which is higher
Description : . In a shell and tube heat exchanger, the tube side heat transfer coefficient just at the entrance of the tube is (A) Infinity (B) Zero (C) Same as average heat transfer co-efficient for tube side (D) None of these
Last Answer : (A) Infinity
Description : Heat transfer by natural convection is enhanced in system with (A) High viscosity (B) High co-efficient of thermal expansio
Last Answer : (B) High co-efficient of thermal expansion
Description : The unit of heat transfer co-efficient in SI unit is (A) J/M2°K (B) W/m2°K (C) W/m°K (D) J/m°K
Last Answer : (B) W/m2°K
Description : Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone. (A) Laminar (B) Transition (C) Both 'a' & 'b' (D) Highly turbulent
Last Answer : (D) Highly turbulent
Description : Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient ... ) Horizontal heat exchanger with steam on tube side (D) Horizontal heat exchanger with steam on shell side
Last Answer : (B) Vertical heat exchanger with steam on shell side
Description : Log mean temperature difference (LMTD) cannot be used, if (A) Heat transfer co-efficient over the entire heat exchanger is not constant (B) There exists an unsteady state (C) The heat capacity is not constant and there is a phase change (D) None of these
Last Answer : (D) None of these
Description : Controlling heat transfer film co-efficient is the one, which offers __________ resistance to heat transfer. (A) No (B) The least (C) The largest (D) Lower
Last Answer : (C) The largest
Description : Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m2°C. (A) 10-50 (B) 100-500 (C) 1000-1500 (D) 5000-15000
Last Answer : (D) 5000-15000
Description : Overall heat transfer co-efficient for cooling of hydrocarbons by water is about (A) 50 -100 Kcal/hr.m2 .°C (B) 50 -100 W/m2 .°K (C) 50 -100 BTU/hr. ft. 2°F (D) 1000 - 1500 BTU/hr. ft. 2°F
Last Answer : (C) 50 -100 BTU/hr. ft. 2°F
Description : Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by h = 0.023 (K/D) (DVρ/µ) 0.8 (CP .µ/k) 0.4 . This is valid for the value of NRe equal to (A) < 2100 (B) 2100-4000 (C) > 4000 (D) > 10000
Last Answer : (D) > 10000
Description : Heat transfer co-efficient (h1 ) for liquids increases with (A) Increasing temperature (B) Decreasing temperature (C) Decreasing Reynolds number (D) None of these
Last Answer : (A) Increasing temperature